Armour class
When something injures you, your Armour class (often abbreviated to AC) reduces the amount of damage you suffer.
The most common way to improve your AC is by wearing armour: body armour, gloves, boots, cloaks, and head gear. Other pieces of gear, especially artefacts, may also increase your AC, and magical spells may temporarily boost it. Heavier body armour (and only body armour) also comes at the cost of EV and spellcasting, though Armour skill can offset its penalties.
AC damage reduction
In general AC reduces the damage of attacks susceptible to AC by an absolute value between 0 and your current AC value. an AC of 10 will reduce damage by a random number between 0 and 10. This applies to damage that would traditionally ignore defense in other games, such as most spell magic and elemental attacks. However, this is not always precisely true. See the AC calculations page for more details.
Guaranteed Damage Reduction
Main Article: GDR
When taking physical damage in melee, guaranteed damage reduction will reduce damage. GDR% is equal to 16*(AC)^1/4. If GDR is applied, the minimum possible AC roll will equal (damage*GDR%) or (AC/2), whichever is lower.
List of attacks or sources of damage which are not reduced by AC
- Torment and Holy Word
- Smite and Damnation
- The poison and sticky flame status effects.
- Extra damage caused by weapon brands, attack flavours and magical staves (except the staff of earth).
- The following spells: Freeze, Pain, Vampiric Draining, Static Discharge, Frozen Ramparts, Ozocubu's Refrigeration.
- The chilling blast breath attack of a white draconian.
